Significance: Aging-associated diseases are increasingly common in an aging global population. However, the contributors and origins of differential risk for unhealthy aging remain poorly understood. Using a mouse model, we found that offspring of aged fathers exhibited a reduced life span and more pronounced aging-associated pathologies than animals sired by young fathers. Tissue of offspring and aged fathers revealed shared epigenetic signatures and showed altered activation states of longevity-related cell signaling. Our results suggest that variability in aging trajectories could derive, in part, from the age at conception of the father, a possibility that warrants human epidemiological investigation.

RORγt is the master transcription factor for the Th17 cells. Paradoxically, in the intestine, RORγt is coexpressed in peripherally induced regulatory T cells (pTregs) together with Foxp3, the master transcription factor for Tregs. Unexpectedly, by an unknown mechanism, colonic RORγt⁺ Tregs show an enhanced suppressor function and prevent intestinal inflammation more efficiently than RORγt-nonexpressing pTregs. Although studies have elucidated the function of RORγt in Th17 cells, how RORγt regulates pTreg function is not understood. In our attempt to understand the role of RORγt in controlling Treg function, we discovered a RORγt-driven pathway that modulates the regulatory (suppressor) function of colonic Tregs. We found that RORγt plays an essential role in maintaining Foxp3 expression. RORγt-deficient Tregs failed to sustain Foxp3 expression with concomitant upregulation of T-bet and IFN-γ expressions. During colitis induced by adoptive transfer of CD45RB^hi cells in Rag1^−/− mice, RORγt-deficient colonic Tregs transitioned to a Th1-like effector phenotype and lost their suppressor function, leading to severe colitis with significant mortality. Accordingly, Foxp3-expressing, RORγt-deficient Tregs showed impaired therapeutic efficacy in ameliorating colitis that is not due to their reduced survival. Moreover, using the Treg-specific RORγt and T-bet double-deficient gene knockout mouse, we demonstrate that deletion of T-bet from RORγt-deficient Tregs restored Foxp3 expression and suppression function as well as prevented onset of severe colitis. Mechanistically, our study suggests that RORγt-mediated repression of T-bet is critical to regulating the immunosuppressive function of colonic Tregs during the inflammatory condition. Key Points In the absence of RORγt, colonic Tregs lose Foxp3 expression and suppressor function. RORγt promotes Foxp3 expression by antagonizing effector fate of colonic Tregs. RORγt represses T-bet to control the suppressor function of Tregs.

The effect of Alzheimer’s disease (AD) medications on CD4+ T cells homing has not been thoroughly investigated. CD4+ T cells could both exacerbate and reduce AD symptoms based on their infiltrating subpopulations. Proinflammatory subpopulations such as Th1 and Th17 constitute a major source of proinflammatory cytokines that reduce endothelial integrity and stimulate astrocytes, resulting in the production of amyloid β. Anti-inflammatory subpopulations such as Th2 and Tregs reduce inflammation and regulate the function of Th1 and Th17. Recently, pathogenic Th17 has been shown to have a superior infiltrating capacity compared to other major CD4+ T cell subpopulations. Alzheimer’s drugs such as donepezil (Aricept), rivastigmine (Exelon), galantamine (Razadyne), and memantine (Namenda) are known to play an important part in regulating the mechanisms of the neurotransmitters. However, little is known about the effect of these drugs on CD4+ T cell subpopulations’ infiltration of the brain during AD. In this review, we focus on understanding the influence of AD drugs on CD4+ T cell subpopulation interactions with the BBB in AD. While current AD therapies improve endothelial integrity and reduce astrocytes activations, they vary according to their influence on various CD4+ T cell subpopulations. Donepezil reduces the numbers of Th1 but not Th2, Rivastigmine inhibits Th1 and Th17 but not Th2, and memantine reduces Th1 but not Treg. However, none of the current AD drugs is specifically designed to target the dysregulated balance in the Th17/Treg axis. Future drug design approaches should specifically consider inhibiting CD4+ Th17 to improve AD prognosis.

Understanding the evolution of interleukins and interleukin receptors is essential to control the function of CD4+ T cells in various pathologies. Numerous aspects of CD4+ T cells’ presence are controlled by interleukins including differentiation, proliferation, and plasticity. CD4+ T cells have emerged during the divergence of jawed vertebrates. However, little is known about the evolution of interleukins and their origin. We traced the evolution of interleukins and their receptors from Placozoa to primates. We performed phylogenetic analysis, ancestral reconstruction, HH search, and positive selection analysis. Our results indicated that various interleukins’ emergence predated CD4+ T cells divergence. IL14 was the most ancient interleukin with homologs in fungi. Invertebrates also expressed various interleukins such as IL41 and IL16. Several interleukin receptors also appeared before CD4+ T cells divergence. Interestingly IL17RA and IL17RD, which are known to play a fundamental role in Th17 CD4+ T cells first appeared in mollusks. Furthermore, our investigations showed that there is not any single gene family that could be the parent group of interleukins. We postulate that several groups have diverged from older existing cytokines such as IL4 from TGFβ, IL10 from IFN, and IL28 from BCAM. Interleukin receptors were less divergent than interleukins. We found that IL1R, IL7R might have diverged from a common invertebrate protein that contained TIR domains, conversely, IL2R, IL4R and IL6R might have emerged from a common invertebrate ancestor that possessed a fibronectin domain. IL8R seems to be a GPCR that belongs to the rhodopsin-like family and it has diverged from the Somatostatin group. Interestingly, several interleukins that are known to perform a critical function for CD4+ T cells such as IL6, IL17, and IL1B have gained new functions and evolved under positive selection. Overall evolution of interleukin receptors was not under significant positive selection. Interestingly, eight interleukin families appeared in lampreys, however, only two of them (IL17B, IL17E) evolved under positive selection. This observation indicates that although lampreys have a unique adaptive immune system that lacks CD4+ T cells, they could be utilizing interleukins in homologous mode to that of the vertebrates’ immune system. Overall our study highlights the evolutionary heterogeneity within the interleukins and their receptor superfamilies and thus does not support the theory that interleukins evolved solely in jawed vertebrates to support T cell function. Conversely, some of the members are likely to play conserved functions in the innate immune system.

Neurobehavioral disorders and brain abnormalities have been extensively reported in both Crohn’s disease and ulcerative colitis patients. However, the mechanism causing neuropathological disorders in inflammatory bowel disease patients remains unknown. Studies have linked the Th17 subset of CD4+ T cells to brain diseases associated with neuroinflammation and cognitive impairment, including multiple sclerosis, ischemic brain injury, and Alzheimer’s disease. To better understand how CD4+ T lymphocytes contribute to brain pathology in chronic intestinal inflammation, we investigated the development of brain inflammation in the T cell transfer model of chronic colitis. Our findings demonstrate that CD4+ T cells infiltrate the brain of colitic Rag1−/− mice in proportional levels to colitis severity. Colitic mice developed hypothalamic astrogliosis that correlated with neurobehavioral disorders. Moreover, the brain-infiltrating CD4+ T cells expressed Th17 cell transcription factor retinoic acid–related orphan receptor γt (RORγt) and displayed a pathogenic Th17 cellular phenotype similar to colonic Th17 cells. Adoptive transfer of RORγt-deficient naive CD4+ T cells failed to cause brain inflammation and neurobehavioral disorders in Rag1−/− recipients, with significantly less brain infiltration of CD4+ T cells. The finding is mirrored in chronic dextran sulfate sodium–induced colitis in Rorcfl/fl Cd4-Cre mice that showed lower frequency of brain-infiltrating CD4+ T cells and astrogliosis despite onset of significantly more severe colitis compared with wild-type mice. These findings suggest that pathogenic RORγt+CD4+ T cells that aggravate colitis migrate preferentially into the brain, contributing to brain inflammation and neurobehavioral disorders, thereby linking colitis severity to neuroinflammation.

The use of single‐cell RNA sequencing (scRNA‐seq) in microglial research is increasing rapidly. The basic workflow of this approach consists of isolating single cells, followed by sequencing. scRNA‐seq is capable of examining microglial heterogeneity on a cellular level. However, the results gained from applying this technique suffer from discrepancies due to differences between applied methods characteristics such as the number of cells sequenced and the depth of sequencing. This review aims to shed more light on the recent developments that happened in this field and how they are related to the methods used. To do that, we track the progress and limitations of various scRNA‐seq methods currently available. The review then summarizes the current knowledge gained using scRNA‐seq in the field of microglia, including novel subpopulations associated with function and development under homeostasis as well during several pathological conditions such as Alzheimer, lipopolysaccharide response, and HIV in relation to the methods employed. Our review points out that despite major developments found using this technique, current scRNA‐seq methods suffer from high cost, low yields, and nonstandardization of generated data. Additional development of scRNA‐seq methods will raise our awareness of microglia's heterogeneity and plasticity under healthy and pathological conditions.